1. Field of the Invention
The present invention relates to a multi-database system where databases are present in a distributed form. Among others, the present invention relates to security for the disclosure of information of the multi-database system. The present invention, more particularly, relates to a secure multi-database system in which a plurality of databases are operated in an federating manner and security for individual databases is ensured, and an information mediation system on a network to which such a system is applied.
2. Description of the Related Art
Currently, as a technique for getting access to a multi-database (MDB) system, there has been known a technique which gets access to a table (an external table) of an external database (external DB) through an external data wrapper. In this technique, a user declares an access method to the external DB or the configuration of the external table to the MDB system. In the MDB system, the external table is handled in the same manner as a usual view table and it is possible for the user to declare a view table which combines external tables together or a view table which combines the external table with a table inside the MDB system (an internal table).
ISO/IEC standardizes the architecture and a database language of this MDB system as “Database Language SQL-Part 9: Management of External Data (SQL/MED)” which is a database language SQL having a specification Part 9 for a next generation known as SQL3 or SQL-Part 99. With respect to SQL/MED, a draft of ISO/IEC is laid open to the public and as an article which interprets ISO/IEC, ACM SIGMOD Record, Vol.29, No.1, March 2000, pp63–67, “SQL Standardization: The Next Steps” is available.
Conventionally, as security for DB, a method which sets an access authority to the data to individual users and controls access to the DB based on such access authority “access control” has been dominantly used. The same goes for the MDB.
Recently, along with the popularization of the Internet, the Intranet and the Extranet, the chances that the user gets access to the DB through the network have been increased. In this case, to protect the query messages and data being transmitted through the network from improper access, there has been proposed a method which transmits the query messages and data after encrypting the query messages and data. As a method for encrypting the query messages, U.S. Pat. No. 5,713,018 discloses “SYSTEM AND METHOD FOR PROVIDING SAFE SQL-LEVEL ACCESS TO A DATABASE”. Further, as a method for processing data by encrypting the data on a DBMS, U.S. Pat. No. 5,963,642 discloses “METHOD AND APPARATUS FOR SECURE STORAGE OF DATA”.
Further, as an example which adopts a multi-database system as an information mediation business on the Internet, “Yodlee.com” is known. This business is a service which provides the service details which individual service providers provide in a form that the service details are integrated into one. The user can get the reference of all of the service details by merely getting access to Yodlee.com and hence, it is unnecessary for the user to get access to individual service providers. Yodlee.com regards individual service providers as information sources and performs inquiries of the service details to the service providers while setting respective users as keys and integrates and provides the results of inquiries to the users. Here, although the acquired service details are cached in an internal DB, security is ensured by encrypting the data of this internal DB.